A possible extratubular origin of epididymal basal cells in mice.

The origin of basal cells in mouse epididymis was examined by counting the numbers of basal cells, intratubular mitotic figures and peritubular cells during development of the epididymis. Putative precursors of basal cells were labelled with bromodeoxyuridine and the nuclei of daughter cells were examined. Histochemical localization of cytokines was performed to gauge their involvement in migration of basal cell precursors from extratubular sources. The results indicate that basal cells may arise from extratubular sources as: (i) there was a decrease in the number of mitotic figures as the number of basal cells increased; (ii) no mitotic figures were observed in the base of the epithelium; (iii) the increase in the number of peritubular cells did not parallel the number of basal cells in all epididymal regions; (iv) division of epithelial cells into daughter cells was circumferential and not radial; (v) bromodeoxyuridine-labelled basal cell nuclei were mostly not found in the vicinity of labelled principal cell nuclei and vice versa; and (vi) the percentage of labelled basal cell nuclei was higher than that of the other cells, which is indicative of their arrival from a more highly labelled pool. In addition, no age-dependent correlation was noted between any of the cytokines tested and appearance of basal cells in the epithelium, and basal cells expressed intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1), which provides further evidence of a relationship between basal cells and immunocytes. If basal cells have an immunological function, failure of their recruitment into the epididymal epithelium at about the time of puberty may have repercussions for immunological protection of spermatozoa and, ultimately, for fertility in the adult.